feat(contacts): revamp edit dialog with live preview + avatar picker

Rebuild the add/edit contact dialog on the portfolio-editor design language:

- A live preview card at the top shows the contact exactly as it renders in the
  list (avatar + name + address), updating as you type and pick an avatar.
- An avatar picker (Badge / Icon / Image segmented control) lets you keep the
  default Z/T type badge, choose a Material wallet icon from a searchable grid,
  or set a custom image. The picker area is fixed-height so the modal doesn't
  jump when switching modes.
- Custom images go through a new in-app ImagePicker (image_picker.h): a
  Material overlay that browses the filesystem starting at the user's Pictures
  folder, shows a thumbnail grid (decoded to raw pixels, box-downscaled to a
  small texture, cached per directory and freed on navigate/close, budgeted a
  few decodes per frame so large folders don't hitch), and returns the chosen
  path. The chosen image is copied into <config>/contact-avatars/ (named by an
  FNV hash of the source path, so re-picking is idempotent) and stored as
  "img:<path>". Like FolderPicker, it takes over the modal surface while open.
- Paste is now available on both add and edit; buttons are content-sized.

Adds three sweep surfaces (contacts-edit-{icon,badge,image}) that open the
dialog on a seeded contact in each avatar mode, plus i18n keys (+ 8-language
translations; reworded two zh/ja strings to stay within the existing CJK
subset, so no font rebuild).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

res/lang/es.json

@@ -287,9 +287,20 @@
     "console_welcome": "Bienvenido a la Consola de ObsidianDragon",
     "console_zoom_in": "Acercar",
     "console_zoom_out": "Alejar",
+    "contact_avatar": "AVATAR",
+    "contact_avatar_badge": "Insignia",
+    "contact_avatar_badge_hint": "Usa la insignia de tipo de dirección: Z para blindada, T para transparente.",
+    "contact_avatar_choose": "Elegir imagen…",
+    "contact_avatar_copy_failed": "No se pudo copiar esa imagen.",
+    "contact_avatar_icon": "Icono",
+    "contact_avatar_image": "Imagen",
+    "contact_avatar_image_hint": "La imagen se copia en la app para que siga disponible si el original se mueve.",
+    "contact_avatar_remove": "Quitar",
     "contact_global": "Mostrar en todas las carteras (contacto global)",
     "contact_global_badge_tt": "Contacto global — visible en todas las carteras",
     "contact_global_tt": "Activado: este contacto permanece visible sin importar qué cartera cargues. Desactivado: pertenece solo a la cartera actual.",
+    "contact_preview_addr": "La dirección aparecerá aquí",
+    "contact_preview_name": "Nombre del contacto",
     "contacts": "Contactos",
     "contacts_search_no_match": "No hay contactos coincidentes",
     "contacts_search_placeholder": "Buscar contactos...",
@@ -465,6 +476,12 @@
     "hide_qr": "Ocultar QR",
     "hide_zero_balances": "Ocultar saldos 0",
     "history": "Historial",
+    "img_picker_count": "%d imagen(es) en esta carpeta",
+    "img_picker_empty": "Esta carpeta no tiene subcarpetas ni imágenes.",
+    "img_picker_none": "No hay imágenes en esta carpeta",
+    "img_picker_pictures": "Carpeta de imágenes",
+    "img_picker_title": "Elegir una imagen",
+    "img_picker_use": "Usar imagen",
     "immature_type": "Inmaduro",
     "import": "Importar",
     "import_key_address": "Dirección:",